The present invention relates to an imaging device and, particularly, to such a device using a CCD, charge-coupled device (CCD) which can reduce a noise caused by heat generated by the CCD even when it is exposed for a long time and can read out an image at high speed.
A chemiluminescent detecting system is known, which comprises the steps of selectively labeling a fixed high molecular substance such as a protein or a nucleic acid sequence with a labeling substance which generates chemiluminescent emission when it contacts a chemiluminescent substance, contacting the high molecular substance selectively labeled with the labeling substance and the chemiluminescent substance, photoelectrically detecting the chemiluminescent emission in the wavelength of visible light generated by the contact of the chemiluminescent substance and the labeling substance and producing digital image signals, effecting image processing thereon, and reproducing a chemiluminescent image on a display means such as a CRT or a recording material such as a photographic film, thereby obtaining information relating to the high molecular substance such as genetic information.
Further, a fluorescence system using a fluorescent substance as a labeling substance is known. According to this system, it is possible to study a genetic sequence, the expression level of a gene and the metabolism, absorption, excretion path and state of a substance introduced into a test mouse and to effect separation or identification of protein or estimation of the molecular weight or properties of protein or the like. For example, this system can perform a process including the steps of distributing a plurality of DNA fragments on a gel support by means of electrophoresis after a fluorescent dye was added to a solution containing a plurality of DNA fragments to be distributed or distributing a plurality of DNA fragments on a gel support containing fluorescent dye or dipping a gel support on which a plurality of DNA fragments have been distributed by means of electrophoresis in a solution containing fluorescent dye, thereby labeling the electrophoresis-distributed DNA fragments, exciting the fluorescent dye by a stimulating ray to cause it to release a fluorescent light, detecting the released fluorescent light to produce an image and detecting the distribution of the DNA on the gel support. This system can also perform a process including the steps of distributing a plurality of DNA fragments on a gel support by means of electrophoresis, denaturing the DNA, transferring at least a part of the denatured DNA fragments onto a transfer support such as a nitrocellulose support by the Southern-blotting method, hybridizing a probe prepared by labeling target DNA and DNA or RNA complementary thereto with the denatured DNA fragments, thereby selectively labeling only the DNA fragments complementary to the probe DNA or probe RNA, exciting the fluorescent dye by a stimulating ray to cause it to release a fluorescent light, detecting the released fluorescent light to produce an image and detecting the distribution of the target DNA on the transfer support. This system can further perform a process including the steps of preparing a DNA probe complementary to DNA containing a target gene labeled by a labeling substance, hybridizing it with DNA on a transfer support, combining an enzyme with the complementary DNA labeled by a labeling substance, causing the enzyme to contact a fluorescent substrate, transforming the fluorescent substrate to a fluorescent substance having a fluorescent light releasing property, exciting the thus produced fluorescent substance by a stimulating ray to release fluorescent light, detecting the fluorescent light to produce an image and detecting the distribution of the target DNA on the transfer support. This fluorescence detecting system is advantageous in that a genetic sequence or the like can be easily detected without using a radioactive substance.
In the case where such a chemiluminescent emission or fluorescent light is detected by an imaging device using a CCD to produce a chemiluminescent image or a fluorescent image, since chemiluminescent emission or fluorescent light is very weak, the CCD has to be exposed thereto for a long time. However, it is known that when the CCD is exposed for a long time, noise is generated in the image by heat emitted from the CCD. Therefore, the imaging device for detecting very weak light such as chemiluminescent emission or fluorescent light is provided with a cooling means for cooling the CCD in order to reduce such noise caused by the heat.
Since the trend is to use CCDs with larger number of pixels for obtaining high quality images, however, the power consumed by the output amplifier inevitably increases for reading out image data at high speed from a CCD that may have more than one million pixels. Therefore, since a larger quantity of heat is generated, even if the CCD is cooled by a cooling means, it is difficult to reduce noise caused by heat generated by the CCD in an image.
Similar problems occur when very weak light is detected by a solid state image sensor to produce an image for observing a heavenly body or the like.
It is therefore an object of the present invention to provide an imaging device using a CCD, which can reduce noise caused by heat generated by the CCD even when it is exposed for a long time, and a device which can, read out an image at high speed.
The above and other objects of the present invention can be accomplished by an imaging device comprising a power control means for reducing power fed to an output amplifier of a CCD during exposure of the CCD and restoring the power fed to the output amplifier to the level before reduction a predetermined time period before an image signal produced by the CCD is transferred, and correcting means for correcting offset of the output amplifier based on an output signal output from the output amplifier after restoration of the power fed to the output amplifier and before the transfer of the image signal.
In a preferred embodiment the present invention, the power control means is constituted so as not to feed power to the output amplifier when the CCD is being exposed.
The above and other objects and features of the present invention will become apparent from the following description made with reference to the accompanying drawings.